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为降低过采样后峰均比回升对预留载波法峰均比抑制效果的影响,提出了一种改进方法。该方法利用改进的互熵法计算预留载波的位置,获得一个过采样条件下旁瓣值最低的时域核。用时域核对过采样后的正交频分复用(OFDM)符号进行迭代削峰处理。每次迭代中,OFDM符号的幅度峰值被加权且循环移位后的时域核削减到一个预先设定的阈值。仿真结果表明,该方法可有效降低峰均比回升的影响,在总载波数1 024,预留载波数10的条件下,峰均比抑制效果改善了2.1 dB。 相似文献
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针对正交频分复用(OFDM)系统的高峰均功率比问题,介绍了一种改进的载波保留(TR)方法,该算法应用时域核函数构造时域核函数矩阵并进行缩放参数优化,迭代过程复杂度低且性能良好.设计了一种简化的OFDM发射机方案以验证该算法在实际系统中的有效性,给出了在FPGA上实现该方案的整体架构及关键模块.硬件测试结果表明该OFDM发射机的峰均比得到了有效抑制,验证了该TR算法的正确性,证明其有较好的应用前景. 相似文献
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介绍了单载波频域均衡技术的原理,与单载波时域均衡以及多载波OFDM系统进行了比较。该技术结合了两者的优点:能有效对抗多径信道,且具有较低的复杂度;降低了峰均比和对载波频偏、相位噪声的敏感性,因而在无线通信领域具有广阔的应用前景。 相似文献
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将载波干涉码引入OFDM系统,可以提高误码性能,并消除峰均功率比问题。该文从数学角度证明了载波干涉OFDM系统与现有的单载波频域均衡系统其实等同。 相似文献
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多载波调制中降低峰均比问题的研究 总被引:1,自引:0,他引:1
多载波调制技术由于具有极高的频谱利用率和有效的抗码问干扰性能,特别适用于无线环境下的高速传输,被普遍认为是下一代无线通信系统必不可少的技术.但是它的一个主要缺点是峰均功率比(PAPR)特别高,会给系统设计带来很多问题.讨论了高峰均功率比产生的原因及其对多载波通信性能影响,分析了几种抑制高峰均比的方法和其特点.研究了选择性映射降低峰均功率比算法及其改进方法,探讨了多载波系统PAPR的性能. 相似文献
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首先分析了基于载波抑制归零码的光载波抑制归零-开关键控(CSRZ-OOK)、载波抑制归零-差分相移键控(CSRZ-DPSK)和载波抑制归零-差分正交相移键控(CSRZ-DQPSK) 三种光调制格式的时域和频域特性,并数字仿真了其在40 Gbit/s单信道光纤系统中的传输性能.以Q值、眼图和误码率(BER)作为性能评价指标,研究了这三种调制格式对色散(CD)、偏振模色散(PMD)和非线性效应的抑制作用.结果表明:CSRZ-DQPSK相对于CSRZ-OOK、CSRZ-DPSK对色散、偏振模色散和非线性效应有非常好的容忍能力. 相似文献
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时频二维重叠复用系统 总被引:1,自引:0,他引:1
基于时域重叠复用和频域重叠复用的思想,该文提出了时频二维重叠复用系统OvHDM系统。研究了OvHDM系统的最佳检测、频谱效率、复杂度、性能以及峰均比。OvHDM系统模型是向量卷积编码约束模型。为了检测OvHDM信号,提出了向量空间上的最大似然序列检测算法,MU-MLSD。计算机仿真证明:频谱效率为 时,OvHDM较64QAM具有4.5dB的功率增益,较OvTDM也有1.5dB的功率增益;同时,OvHDM的峰均比较128个子载波的OFDM有2dB的增益,较1024个子载波的OFDM有2.6dB的增益。 相似文献
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高峰均功率比一直是掣肘OFDM系统性能的最大障碍。为了更精确地评估峰均比抑制对功放失真的影响,提出了最优CCDF(OCCDF)迭代收敛准则。新准则考虑放大器中每个子载波的失真,限定MER条件下得到尽可能低的放大器输入功率回退(IBO),获得最高功放效率所匹配的OFDM整体信号分布。基于此,在CMMB系统中给出了一种高效的时域削波结合星座图扩展(ACE)的峰均比抑制技术。采用OCCDF迭代峰均比抑制方案实验结果:MER=40 dB条件下,基于ACE峰均比抑制的OFDM系统相比抑制前获得了3.05 dB的功放IBO性能改善。对应到功率放大器的性能改善:功放效率提升了15.74%,总功耗和管耗分别降低了22.2%和40.19%。 相似文献
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基于STBC方案,针对MIMO OFDM通信系统中同时存在发射机和接收机I/Q不平衡、前端滤波器失配、CFO和频率选择性信道失真的组合影响进行了深入研究,并提出了一种适用的联合均衡策略;具体实现是首先通过对MIMO OFDM系统中只存在发射机I/Q不平衡和多径信道干扰的分析,得到一种频域均衡器;然后再考虑同时存在接收机I/Q不平衡和CFO的情况,得到了2个时域均衡器;最后把2个时域均衡器变换到频域,并结合消除发射机I/Q不平衡和多径信道干扰的频域均衡技术,提出了一种全面的联合均衡技术即频域子载波均衡器。仿真结果表明,针对MIMO OFDM系统提出的频域子载波均衡技术不仅能扩展到其他高阶STBC系统,而且使均衡后的系统BER性能得到了明显的提高。 相似文献
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Low Complexity Discrete Hartley Transform Precoded OFDM System over Frequency‐Selective Fading Channel
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Orthogonal frequency‐division multiplexing (OFDM) suffers from spectral nulls of frequency‐selective fading channels. Linear precoded (LP‐) OFDM is an effective method that guarantees symbol detectability by spreading the frequency‐domain symbols over the whole spectrum. This paper proposes a computationally efficient and low‐cost implementation for discrete Hartley transform (DHT) precoded OFDM systems. Compared to conventional DHT‐OFDM systems, at the transmitter, both the DHT and the inverse discrete Fourier transform are replaced by a one‐level butterfly structure that involves only one addition per symbol to generate the time‐domain DHT‐OFDM signal. At the receiver, only the DHT is required to recover the distorted signal with a single‐tap equalizer in contrast to both the DHT and the DFT in the conventional DHT‐OFDM. Theoretical analysis of DHT‐OFDM with linear equalizers is presented and confirmed by numerical simulation. It is shown that the proposed DHT‐OFDM system achieves similar performance when compared to other LP‐OFDMs but exhibits a lower implementation complexity and peak‐to‐average power ratio. 相似文献
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Khaled Ramadan Khalil F. Ramadan Ahmed S. Fiky Hasna Alam Moawad I. Dessouky Fathi E. Abd El‐Samie 《International Journal of Communication Systems》2020,33(3)
Frequency synchronization has a great importance in preserving the performance of the underwater acoustic (UWA) orthogonal frequency division multiplexing (OFDM) systems. The carrier frequency offset (CFO) estimation can be blind or data‐aided. In this paper, the Zadoff‐Chu (ZC) sequences are used for OFDM synchronization in UWA communications, and they are compared with different data‐aided algorithms. We propose a low‐complexity algorithm for CFO estimation based on ZC sequences. Also, a joint equalization and CFO compensation scheme for UWA‐OFDM communication systems is presented. Simulation results demonstrate that the proposed CFO estimation algorithm allows estimation of the CFO accurately with a simple implementation in comparison with the traditional schemes. Also, the performance of the UWA‐OFDM system can be preserved in the presence of frequency offsets. 相似文献
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A time-frequency decision-feedback loop for carrier frequency offset tracking in OFDM systems 总被引:1,自引:0,他引:1
Linling Kuang Zuyao Ni Jianhua Lu Junli Zheng 《Wireless Communications, IEEE Transactions on》2005,4(2):367-373
Acquisition and tracking are two crucial stages necessary to the carrier frequency synchronization in orthogonal frequency division multiplexing (OFDM) systems. In this letter, by employing the rotation property of OFDM data subcarriers, a simple time-frequency decision-feedback loop without the use of pilot subcarriers is proposed for the fine carrier frequency offset (CFO) tracking. Specifically, with proper loop parameters, a residual CFO less than 10% of the subcarrier spacing may be well tracked for quarternary phase-shift keying (QPSK) modulation in the presence of noise, while for systems using QPSK, 16-QAM, and 64-QAM modulation schemes, the bit-error rate (BER) performance very close to that of an offset-free system may be achieved in both additive white Gaussian noise (AWGN) and frequency selective fading channels. Moreover, a hardware implementation in a practical OFDM system is fulfilled which verifies the effectiveness of the proposed scheme. 相似文献
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针对正交频分复用(OFDM)系统中的信道时变,基于时变信道的分段线性近似模型,提出一种改进的OFDM时变信道估计方案。该方案通过采用期望最大化(EM)迭代算法来提高符号平均信道脉冲响应的估计精度,从而提高时变信道估计的性能;此外,在迭代过程中进行带状子载波间干扰抑制,不仅进一步提高了时变信道估计的性能,而且降低了实现复杂度。理论分析和仿真结果表明,该算法以较低的复杂度代价有效提高了时变信道OFDM系统的性能。 相似文献
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MIMO OFDM Receivers for Systems With IQ Imbalances 总被引:2,自引:0,他引:2
《Signal Processing, IEEE Transactions on》2005,53(9):3583-3596
Orthogonal frequency division multiplexing (OFDM) is a widely recognized modulation scheme for high data rate communications. However, the implementation of OFDM-based systems suffers from in-phase and quadrature-phase (IQ) imbalances in the front-end analog processing. Such imbalances are caused by the analog processing of the received radio frequency (RF) signal, and they cannot be efficiently or entirely eliminated in the analog domain. The resulting IQ distortion limits the achievable operating SNR at the receiver and, consequently, the achievable data rates. The issue of IQ imbalances is even more severe at higher SNR and higher carrier frequencies. In this paper, the effect of IQ imbalances on multi-input multioutput (MIMO) OFDM systems is studied, and a framework for combating such distortions through digital signal processing is developed. An input–output relation governing MIMO OFDM systems is derived. The framework is used to design receiver algorithms with compensation for IQ imbalances. It is shown that the complexity of the system at the receiver grows from dimension$(n_Rtimes n_T)$ for ideal IQ branches to$(2n_Rtimes 2n_T)$ in the presence of IQ imbalances. However, by exploiting the structure of space-time block codes along with the distortion models, one can obtain efficient receivers that are robust to IQ imbalances. Simulation results show significant improvement in the achievable BER of the proposed MIMO receivers for space-time block-coded OFDM systems in the presence of IQ imbalances. 相似文献
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Multiuser MIMO OFDM Based TDD/TDMA for Next Generation Wireless Communication Systems 总被引:1,自引:1,他引:0
Multiple-input multiple-output (MIMO) wireless technology in combination with orthogonal frequency division multiplexing (MIMO
OFDM) is an attractive air-interface solution for next-generation wireless local area networks (WLANs), wireless metropolitan
area networks (WMANs), and fourth-generation mobile cellular wireless systems. In this paper, one multiuser MIMO OFDM systems
with TDD/TDMA was proposed for next-generation wireless mobile communications, i.e., TDD/TDMA 4G, which can avoid or alleviate
the specific limitations of existing techniques designed for multiuser MIMO OFDM systems in broadband wireless mobile channel
scenarios, i.e., bad performance and extreme complexity of multiuser detectors for rank-deficient multiuser MIMO OFDM systems
with CDMA as access modes, extreme challenges of spatial MIMO channel estimators in rank-deficient MIMO OFDM systems, and
exponential growth complexity of optimal sub-carrier allocations for OFDMA-based MIMO OFDM systems. Furthermore, inspired
from the Steiner channel estimation method in multi-user CDMA uplink wireless channels, we proposed a new design scheme of
training sequence in time domain to conduct channel estimation. Training sequences of different transmit antennas can be simply
obtained by truncating the circular extension of one basic training sequence, and the pilot matrix assembled by these training
sequences is one circular matrix with good reversibility. A novel eigenmode transmission was also given in this paper, and
data symbols encoded by space–time codes can be steered to these eigenmodes similar to MIMO wireless communication systems
with single-carrier transmission. At the same time,, an improved water-filling scheme was also described for determining the
optimal transmit powers for orthogonal eigenmodes. The classical water-filling strategy is firstly adopted to determine the
optimal power allocation and correspondent bit numbers for every eigenmode, followed by a residual power reallocation to further
determine the additional bit numbers carried by every eigenmode. Compared with classical water-filling schemes, it can also
obtain larger throughputs via residual power allocation. At last, three typical implementation schemes of multiuser MIMO OFDM
with TDMA, CDMA and OFDMA, i.e., TDD/TDMA 4G, VSF-OFCDM and FuTURE B3G TDD, were tested by numerical simulations. Results
indicated that the proposed multiuser MIMO OFDM system schemes with TDD/TDMA, i.e., TDD/TDMA 4G, can achieve comparable system
performance and throughputs with low complexity and radio resource overhead to that of DoCoMo MIMO VSF-OFCDM and FuTURE B3G
TDD. 相似文献